Double-insulated spark plug



July 8, 1924.

A. J. CHAMPION DOUBLE lNSULATED SPARK PLUG Filed Nov. 24 1919 Patented Julys, 1924. i i 1,501,021

UNITED STATES PATENT OFFICE.

ALBERT J'. CHAMPION, 0F FLINT, MICHIGAN, ASSIGNORTO A C SPARK PLUG COMPANY, OF FLINT, MICHIGAN, A CORPORATION OF MICHIGAN.

DOUBLE-INSULATED SPARK PLUG.

Application led November 24, 1919. Serial No. 340,102.

T all w 710m t may Game7-n; post indicated by the reference numeral 7, in

Be it known that I, ALBERT J. CHAMPION, order to facilitate the connection of a cona citizen of the United States, and a resiductor with the plug and through which dent of Flint, county of Genesee, and State current maybe supported thereto.

of Michigan, have invented certain new and Referring first to the` form of my invention 50 useful Improvements in Double-Insulated illustrated in Figure 1, the porcelain orequiv- Spark Plugs, of which the following is a alent insulating member is itself supported full, lclear, concise, and exact description, by va suitable metallic supporting member 8 such as will enable others skilled in the art Shown as in the form of a sleeve or bushing 1010 which the invention relates to make and surrounding the same and within which the, 65 use the same, reference being made therein insulator is secured and whereby the same is to the accompanying drawings, which form supported. The lower end of the bushing 8 a part of this specification. 1S provided with an inturned flange or ledge My invention relates to spark plugs de- 9 against which a shoulder of the insulator signed for use with internal combustion enrests, a suitable cushion being interposed be- 70 gines to ignite the combustible mixture withtween the elements referred -to in order to in the cylinder thereof; and the object of reduce the liability of breaking the porcelain my invention is to provide a spark plug 1n assembling the plug. In the form of m which will be more effectively insulated than invention illustrated the upper end 10 ofthe has heretofore commonly been the case, and bushing .S is turned inward and over a 75 a spark plug which when in use will be less shoulder 11 formed upon the insulating liable to become short circuited than has member to thereby permanently secure the heretofore been the case in spark plugs of lnsulator in place within the metallic sleeve the form and construction .at present com- Or bushing whereby it is supported, a suitmonly employed and wherein the external able cushion being interposed between the 30 shell orcasing of the plug which carries the parts to prevent the breaking of the porce-- outer electrode is grounded upon. the engine lain. The cushions here referred to may be structure, and is in directl metallic Contact made of various materials, altho I prefer to with the insulator of the plug whereby the form them from asbestos, or asbestos eninner electrode is insulated. closed in a thin sheet copper covering as in 85 My invention is shown in its .preferred the case of the usual yieldable metallic faced embodiment in the -drawing accompanyinv gaskets commonly used in and about interand forming a part of this specification, an nal combustion engines. It will be apprewherein; ciated, however, that the porcelain or equiva- Figure 1 is a view showing a spark plug lent insulator neednot be permanently se-v 90 partly in elevation and partly in section; vacured in place within the sleeve or bushing rions portions thereof being broken away which supports 1t, but on the contrary may in order to bring out the features of c0n be held in place by a gland nut similar to the struction ofthe plug as a whole. nut hereinafter referred to to secure the Figure2 is a similar view showing aspark bushing within the shell or casing of the 95 plug modified as to some of the elements plug, or otherwise, should such a construcandvfeatures thereof. tion or constructions be deemed necessary or Referring now to the drawing, the referdesirable. ence numeral 5 designates the main insulator The sleeve or bushing 8 together with the of a spark plug, the same being made com- 'insulator supported within the same is nit- 100 monly of porcelain or similar vitreous maself supported within an external metallic terial, althdmy invention is in no way conshell or casing indicated as a whole by the cerned with the particular material from reference'numeral 12 and which carries the which the insulator is madefand any suitouter or grounded electrode '21 of the plug,

able material may be employed for that said shell or casing being provided with a. 105 urpose. The insulator is provided with a threaded portion 13 at its` lower end Ain lbngitudinally extending passage` through order that it may be screwed into an openwhich the inner electrode 6 of the plug exing provided inthe cylinder of the en ine tends, the u'pper end of said electrode bewith which the" plug is used; while' the ing electrically connected with a binding upperend of said casing or equivalent sup, 110

port is provided with a recess 14 shown as conical in form to conform with the conical outer surface of thebushing` 8 above. referredto. The bushing, together with the insulating member carried by it, Amay `be secured in place within `ythe conical recess in any way as, for example, by means of a gland nut 15 in threaded engagement with a threaded upper portion of the casing 12; and suitable insulating material indicated Iby the reference numerals 16, 17 is interposed betweenthe conicaly peripheral surface of the bushing 8 and the internal wall of the recess 14, and between a shoulder at the upper end of said bushing and an inwardly extending ledge 18 of the gland nut 15; thus providing double insulation, that lis, insulation due to the porcelain or'equivalent material of the main insulator 5 and `due to the insulating material 16, 17, be-

y,tween the inner insulated electrode 6 and or casing, andsurrou-nding the lower endI ofthe insulating member 5. When theplug is in use inert burned gases occupy the space provided bythe annular pocket'19and the yannularspace 20 below it and between the 40` lower end of the insulator and the lower end of the casing and act to prevent the deposit of soot about the insulating member `of the plug yand between the same and the external metallic casing thereof, and the construction in question increases to `an excessive degree the length of the path over which current must travel before the plug can become short circuited. The lower or inner end of the casing is shown as provided with a separate and independent elecv trode 21 the end of which is located close commonl to the inner electrode 6, altho the formation of the inner electrode and of the lower end of the shell may be such that the sparks produced jump from it directl to the outer casing or to a portion thereo and it will be appreciated that the outer electrode is grounded upon the engine because of its connection with the external metallic casing ,of the plug. Y

Heretofore in spark plugsthe insulating member corresponding with the insulator 5 whereby vthe inner electrode is carried has been supported by a metallic Ashell which is itself in direct contact with andis grounded upon the engine when the plug is in use; thus providing a single insulation only between the said electrode and the yground provided by the engine structure. `In such plugs, and because of the fact that thedi-electric strength of the insulating member commonly decreases as the temperature to which the plug is subjected increases, the resistance decreases rapidly upon a rise in temperature and they tend to` become short circuited when they have been heated to any considerable degree, be-

cause of the reductionV inv resistance of the insulating member due to the heating therel of. In my invention, however, the support whereby theinsulator,is'supported is itself insulated from the engine by the layer of,

insulation shown at 16, from which it`vfo1- lows that a double insulation of the inner* from the grounded electrode and ofthe plug* as a whole is secured. Furthermore, thel insulating material 16, as well as thetjointv between the insulator 5 and the sleeve 8 are protected from the effects of the heated gas within the cylinder by the dead gas pocket 19` and thel annular gas space 20 below ltheK same and surrounding the lower end of the i insulator 5, thereby keeping the said insulationcomparatively cool.4 At the same time the insulation in question may be made up of layers of mica or equivalent insulating material, which material cannot, however, be. as readily used in the manufacture of the L main insulator 5 of the plug; thereby providing aplugI in which'not only is 'a double insulation' secured, but a plug in which the two insulating members may-be so Selected and made ofsuch materials as to secure a substantially constant and uniform` resistance to short-circuiting when the `plugis in use; as it is feasible to makeat least one of said insulating materials of a substance which will be affected to a minimum extent by the rise of temperature incident to the use of the plug.`

In the form of my invention illustrated in Figure 2 the inner electrode 22 and the main insulator 23` are substantially the same as in the form of my 'invention illustrated in Figure 1, although the remaining portions of the plug differ somewhat from the forms of corresponding elements present in the plug first herein. described. In this modified form of my invention the metallic supporting sleeve 24 may be made from a. piece of tubing the ends of which are turned inward at 25 to thereby hold the main insulator 23 -in place; and said sleeve, together with the inner insulator and electrode, are held in place within a cylindrical v recess 26 provided in the external metallic casing 27 of the plug `by forcing a ange at the upper end thereof inward, as` shown at 28, thus providing a unitary or one pieceV ias external casing 27 which carries the outer grounded electrode 29 by second insulat ing members l30, thus' providing ,double insulation bet-Ween the two electrodes of the plug; and an annulars'pace 3l is provided between the supporting sleevel and the outer casing which space, however, may be occupied by insulating material, if deemed preferable or desirable.` i

Having thus described and explained my invention, I claim `and desire to ,secure by Letters Patent:

1. In a spark plug,

a'central electrode; anV external metallic shell 'or' casing; a

grounded electrode carried by' said shell;l

double insulation interposed between said inner electrode and said outer shell or casing; and a metallic sleeve interposed between two portions of said double insulation and located out of the path of rthe flow of current between said central ,and grounded electrodes,` and which sleeve serves to support said inner electrode and insulation surrounding the same.

2. In a spark plug, a central insulator; an electrode carried by said insulator; a metallic sleeve or bushing whereby said insulator is supported; an external metallic shell or casing whereby said bushing is supported; an electrode carried by said eX- ternal shell or casing; and an insulatingr material interposed between said external casing1 and said bushing, said metallic and said external shell being inde-v sleeve pendent of one another and each performv said bushing;

pocket within said bushing held; in place within said recess,

. and which bushingx is of less length than said recess so as to provide an annular gas pocket within said casing and between said bushingy and said casing; insulating material interposed between said casing and an insulator located. within bushing and held in place same; andv an electrode carried said sleeve or within the kby said insulator.

In a sparlr plug, an external metallic shell or casing having a threaded lower portion, and a conical recess formed within its upper portion; a metallic sleeve or bushlng conical in form and detachably held in place within theconical recess aforesaid., and which bushing is on less length than said recess so as to provide an annular gas casing and betameen the bushing and the lower end of said recess; insulating material interposed between the interior conical ywall of said casing and said bushing; an insulator located within said sleeve or bushing and permanenti"T held in place Within the same; and an electrode carried by said insulator, i y In testimonyl whereof I aliix my signature. c Y

ALBERT d." CHAMPI inner end, of said Cil 

